JP3502539B2 - Optical memory device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical memory device using evanescent light capable of recording / reproducing information of ultra high density.

[0002]

2. Description of the Related Art Since an optical memory device utilizing evanescent light has been developed in the field of microscopes, first, the technique of a microscope using evanescent waves will be briefly described below.

There is an optical near-field microscope that realizes resolution equal to or less than the wavelength of light by using evanescent waves that do not propagate as probe light. This generates an evanescent wave on the optical probe and detects a change in the field caused by the interaction with the sample, or generates an evanescent wave on the sample surface and brings the optical probe closer to the evanescent wave state. In some cases, the shape of a sample with high resolution is measured by detecting the shape.

The optical near-field microscope can measure the surface shape of a sample with high resolution by utilizing the property that the evanescent wave is non-propagating light and is attenuated at a distance of about the wavelength. Further, the evanescent wave is a light wave having a short wavelength that cannot be realized by ordinary propagating light. The shorter the wavelength of the light wave, the higher the resolution in the lateral direction, so that the optical near-field microscope can perform high-resolution measurement.

The evanescent wave is generated when light is incident from the high-refractive index side to the low-refractive index side at an incident angle equal to or greater than the total reflection angle. Also, when light is incident on a pinhole having a diameter smaller than the wavelength, an evanescent wave is generated on the pinhole. Optical near-field microscopes can be roughly classified into two types according to the method of generating an evanescent wave.
One is a photon tunneling near-field microscope and the other is a pinhole near-field microscope.

The photon tunneling type near-field microscope uses an evanescent wave generated when light is incident on a high refractive index chip or a cover glass at a total reflection angle or more. The photon tunneling near-field microscope can be realized as both a non-scanning type and a scanning type.

Guerra has reported that a non-scanning type photon-tunneling type near-field microscope was realized (Guerra: Appl. Opt., 2).
6,3741, (1990)). According to this, the sample can be directly observed with high resolution by slightly improving the ordinary reflection optical microscope.

Further, a scanning type photon tunneling type near field microscope is disclosed in Courjon (D. Cour).
Jon, K Sarayeddine, and M.M.
Spajer: Optics Commun. , 71,
23 (1989)), Reddic (RC Redd).
ick, R.I. J. Warmack, and T.W. L. F
errell: Phys. Rev. B, 39,767
(1989)), Otsu (Jiang Shuodong, Naoyuki Tomita, Motoichi Otsu,
Optics, Vol. 20, 134 (1991)).

The pinhole type near-field microscope uses a pinhole smaller than the wavelength or an evanescent field generated at the tip of the tip by injecting light into an optical waveguide chip whose tip is sharpened to an area smaller than the wavelength.

It is known that the spot spread of the evanescent field at the tip of the chip hardly spreads up to the penetration length of the evanescent wave. Therefore, pinhole near field microscopes take the form of spot scanning microscopes. This idea came from the 1956 O'Kef
e. (JAO'Keefe: J. Opt. S)
oc. Am. , 45, 359 (1956)), 1972
In 2004, Ash conducted an experiment using microwaves (EA Ash and G. Nicholls: N.
ature, 237, 510 (1972)).

Also, around 1984, the Issacson group (E. Betzig,
A. Lewis, A .; Harootunian, M .; I
ssacson and E. Kratschmer:
Biophys. J. , 49, 269 (1986))
And the group of Pohl of IBM Zurich (D.
W. Pohl, W.D. Denk, and M.D. Lazn
z: Appl. Phys. Lett. , 44,651
(1984)) independently carried out actual instrumentation and experiments.

In the above optical near-field microscope,
Although we have succeeded in improving the resolution in the depth direction in surface shape measurement, it is difficult to improve the resolution in the lateral direction, and very good results have not been obtained. This is because the optical probe in the conventional optical near-field microscope has extremely low efficiency of the light intensity that contributes to the interaction of the sample and the SN ratio in detection is low.

Further, as a conventional probe positioning device, fine positioning is performed by using a piezo element or the like. However, when the sample has a two-dimensional spread, as shown in FIG. High accuracy is required to accurately position the tip of the probe 101 along the sample surface by the probe scanning means 103 such as a piezo element, but each probe scanning means 103 is mechanically independent. Therefore, it is difficult to perform highly accurate scanning. Further, since the dynamic range of the movement amount is narrow, there is a problem that a large sample cannot be measured.

On the other hand, in the optical information recording / reproducing apparatus, there is a problem to improve the recording density of the optical disk memory or the like. For this purpose, it is necessary to collect the probe light used for writing and reading on the recording medium in a small amount. Therefore, in order to collect the probe light in a small amount, an optical pickup using a super-resolution phenomenon has been prototyped (Nikkei Electronics, Volume 528, 124 (199).
1)). The super-resolution phenomenon utilizes the interference of probe light to reduce the spot diameter, but the theoretical limit of the spot diameter is up to 1/2 of the wavelength.

From this theoretical limit, it is necessary to shorten the wavelength of the probe light in order to increase the recording density. But,
In reality, there is a limit to shortening the wavelength of probe light, and there is an overhead in increasing the density. That is, the problem of the conventional optical pickup is that the spot diameter can be reduced to about 1/2 of the wavelength.

Therefore, it has recently been considered to record a signal in an area having a size equal to or smaller than the wavelength of light by using the method of the above-mentioned optical near field microscope (for example, see Japanese Patent Laid-Open No. 7-21564). ) Has not been realized due to the same problems as in the above optical near-field microscope.

By the way, as one method for efficiently generating an evanescent wave at the tip of the probe, a slit type method was published in Proceedings of the 58th Annual Meeting of the Applied Physics Society of Japan, October 1997 (5a-L-5). A millimeter-wave band near-field microscope using a probe is disclosed. This is to increase the power of the generated evanescent wave by making the probe a slit type, and the millimeter wave is used in the experiment. However, since the generated evanescent wave is of the slit type, it cannot be recorded in a small recording pit like the conventional optical memory device.

[0018]

SUMMARY OF THE INVENTION For example, Japanese Patent Laid-Open No. 7-2
An optical memory device applying a so-called P-STM (photon scanning tunneling microscope) that records / reproduces information by using an evanescent wave generated by a photon tunnel phenomenon as proposed in Japanese Patent No. 1564 (or the like) (or , And also referred to as a photon scanning tunneling memory in P-STM), there is a problem that reliable information recording / reproducing cannot be performed because the intensity of the probe light is extremely small, and the probe positioning accuracy, Also, there is a problem that it is difficult to secure the movement amount.

The present invention has been made in view of the above points. First, the intensity of probe light is improved,
Secondly, it is an object of the present invention to provide an optical memory device capable of facilitating the positioning of the probe and greatly improving the dynamic range of the probe movement amount.

[0020]

An optical memory device according to a first aspect of the present invention is an optical memory device for recording / reproducing information on / from an optical recording medium by using evanescent light generated by a tunnel phenomenon of photons. A first probe having a slit-shaped opening for generating evanescent light at the tapered tip and a second probe having a slit-shaped opening for generating evanescent light at the tapered tip. The first probe and the second probe are arranged so as to face each other with the optical recording medium sandwiched therebetween in a state where the slit-shaped openings intersect each other , and the first probe and the second probe are provided. With probe
Located in the area where the evanescent waves generated from
The recording medium portion is used as a recording pit .

As a result, since the first and second probes are arranged to face each other with the optical recording medium sandwiched therebetween,
The evanescent wave having a large power can be concentrated in a minute area at the intersection of the first and second probes, and the intensity of the probe light can be improved.
Therefore, highly reliable recording / reproducing of information can be guaranteed.

An optical memory device according to a second aspect of the present invention is the optical memory device according to the first aspect,
The first and second probes are arranged to face each other with their slit-shaped openings orthogonal to each other.

Since the first and second probes are arranged so as to face each other so that their slit-shaped openings are orthogonal to each other, the area of the concentrated area (recording pit) of the evanescent wave is reduced. Therefore, it is possible to record / reproduce information with high density.

An optical memory device according to a third aspect of the present invention is the optical memory device according to the first or second aspect, wherein the first and second probes are generated from each slit type opening. They are arranged so as to face each other with a gap to the extent that evanescent light does not tunnel.

Thus, the gap between the first and second probes is set so that the evanescent wave does not tunnel, so that a large power evanescent wave can be generated at the center between the two probes. It is possible to record / reproduce information with high density and high reliability.

An optical memory device according to a fourth aspect of the present invention is the optical memory device according to any one of the first to third aspects, wherein the first and second probes are provided with coherent light beams, respectively. It is incident.

Thus, since light having coherence with each other is used as the light incident on the probe, the evanescent waves generated by the first probe and the second probe interfere with each other and have coherence. Since the optical power is increased as compared with the case where non-use light is used, it is possible to more efficiently generate the evanescent wave.

An optical memory device according to a fifth aspect of the present invention is the optical memory device according to any one of the first to fourth aspects, wherein the first and second probes are provided with a slit-shaped opening having a long length. The light is incident on the light having a deflection direction perpendicular to the direction.

Since the deflection direction of the incident light of the probe is perpendicular to the longitudinal direction of each slit type opening, the transmitted light is prevented from being generated at the tip of the probe and only the evanescent wave is generated. Since it is not necessary to change the distance between the probe and the optical recording medium in a sinusoidal shape and to extract only the component that changes in synchronization with the distance during reading (reproduction) as in the conventional example described above. , S / N information can be recorded / reproduced.

An optical memory device according to a sixth aspect of the present invention is the optical memory device according to the first to fifth aspects, wherein the first probe and the second probe are independent of the optical recording medium. A scanning means for one-dimensional scanning is provided.

As a result, since the scanning means for scanning the first and second probes are made to be mechanically independent and one-dimensionally scanned, the respective scanning means do not interfere with each other and the accuracy is high. The probe can be positioned, and the dynamic range of probe scanning can be improved as compared with two-dimensional scanning. Also, 2
Since the mechanism is simpler than the dimensional scanning means, it leads to cost reduction.

[0032]

DETAILED DESCRIPTION OF THE INVENTION A first embodiment of an optical memory device of the present invention will be described below with reference to FIGS.
Here, FIG. 1 is an explanatory diagram showing a schematic configuration of the optical memory device of the present embodiment, FIG. 2 is a schematic explanatory diagram showing a probe of the optical memory device of the present embodiment, and FIG. 3 is an optical recording medium in the optical memory device of the present embodiment. It is a schematic explanatory drawing which shows the recording pit inside.

As shown in FIG. 1, the optical memory device of the present embodiment has two probes 2 and 3 formed of glass fiber or the like, and a probe scanning means (not shown) for scanning the respective probes 2 and 3. And an optical recording medium 4 in which a recording layer containing a photochromic material or the like is formed on a transparent substrate. The two probes 2 and 3 are
As shown in FIG. 2, the tip shape is formed into tapered shapes 8 and 10, and slit-shaped openings 9 and 11 are formed at the tips.
Is provided.

When incident lights 5 and 6 are incident on the probes 2 and 3 having such a structure, evanescent waves are generated near the slit-shaped openings 9 and 11. The existence region of this evanescent wave is very small, and the spread is only about the wavelength. Therefore, it is possible to record laser light in a recording pit that is significantly smaller than the beam waist diameter when a condenser lens is used, as in the conventional CD (compact disc), MD (mini disc), DVD (digital video disc). Become.

The above-mentioned two probes 2 and 3 are arranged so as to face each other with their openings 9 and 11 orthogonal to each other, and the gap between the openings 9 and 11 of each probe 2 and 3 is different. The evanescent waves from the openings 9 and 11 of the probes 2 and 3 are brought close to the limit where they do not propagate to the other probes 3 and 2. Further, the optical recording medium 4 has a reaction darkness value with respect to the light intensity, and the openings 9, 9 of the probes 2, 3 are
It is required to have a thickness that can be inserted into the gap of 11.

Next, the recording mechanism of the optical recording medium 4 will be described with reference to FIG. FIG. 3 shows the XY plane of the optical recording medium 4, and the regions 12 and 13 represent the evanescent wave generation region by the first probe 2 and the evanescent wave generation region by the second probe 3, respectively. Since the optical recording medium 4 has a response value with respect to the change in light intensity, the shaded portions of the regions 12 and 13 are not exposed, and only the overlapping portion 14 of the regions 12 and 13 is exposed.

That is, of the two probes 2 and 3,
The material of the optical recording medium 4 does not change with the evanescent wave power of either one, but the other probe 3, 2
The material changes only when the evanescent wave power due to is applied. The term "photosensitivity" used herein does not mean only the photosensitivity in photographic technology, but it is a general term such as changing an optical constant of a material or exciting electrons by light.

In the present embodiment, the polarization directions of the incident lights 5 and 6 incident on the two probes 2 and 3 are perpendicular to the longitudinal direction of the slit-shaped open portions 9 and 11. As a result, the electric field does not vibrate in the directions of the openings 9 and 11 of the probes 2 and 3, so that transmitted light is not generated from the openings 9 and 11 and only the evanescent wave is generated. Therefore, the optical recording medium 4 by the transmitted light
It is possible to prevent unnecessary recording on the.

Next, the positioning of the optical recording material 4 in the recording pit by scanning with the probes 2 and 3 will be described. As described above, in the optical memory device of this embodiment, the recording material portion located in the region 12 where the evanescent waves generated from the first probe 2 and the second probe 3 intersect becomes a recording pit. Therefore, unlike the conventional example described above with reference to FIG. 5, it is not necessary to perform two-dimensional scanning of the probe in the XY plane.

As described above, in the optical memory device of the present embodiment, the recording pits are recorded at arbitrary positions in the XY plane by scanning the optical recording medium 4 with the probes 2 and 3 one-dimensionally. Can be formed. Further, since the probe scanning means of the present embodiment is constituted by two mechanically independent one-dimensional scanning means, it is possible to perform highly accurate and reliable probe scanning.

Next, reading (reproduction) from the optical recording medium 4 will be described. At the time of writing (recording) information on the optical recording medium 4, the incident light 5 and 6 are simultaneously made incident on the first probe 2 and the second probe 3 as described above. In the case of reading, incident light for reading may be incident on only one of the two probes 2 and 3, and the light from the recording pit of the optical recording medium 4 may be detected by the other probe.

The incident lights 5 and 6 respectively incident on the first probe 2 and the second probe 3 may be completely independent, but the lights generated by the same laser device are divided and used. can do. This will be described with reference to FIG. 4 as a second embodiment of the memory device of the present invention. The same parts as those in the first embodiment described above will be denoted by the same reference numerals and description thereof will be omitted. Here, FIG. 4 is an explanatory diagram showing a schematic configuration of the optical memory device of the present embodiment.

In the present embodiment, as shown in FIG. 4, a beam splitter 22 is provided between a laser device (light source) 21 and each of the probes 2 and 3, and a split light beam split by the beam splitter 22 is used. Are incident lights 5 and 6 of the respective probes 2 and 3. Incidentally, 23
Numerals 25 are mirrors for guiding one output light of the beam splitter 22 to the entrance of the probe 3.

With this structure, the evanescent waves generated from the first probe 2 and the second probe 3 are converted into the propagating light by the optical recording medium 4, and the first and second probes 2 are further converted. , 3 propagates from the same light source 21, the recording area 1 of the optical recording medium 4
4 and the recording light power intensity can be further increased.

In the above-described embodiment of the present invention, the optical recording medium 4 has been described as a disk type, but the shape is not limited to this, and any flat type may be used. Further, it is clear that the tip of the probes 2 and 3 may be scanned over the entire area of the optical recording medium 4 by providing a scanning means for scanning the optical recording medium 4 instead of scanning the probes 2 and 3. Is.

Further, in the above-described embodiment of the present invention, the first
In addition, as the second probes 2 and 3, slit-shaped openings 9 and 11 are provided at the tip end portions of the tapers 8 and 10 in order to maintain the strength, but a structure for generating an evanescent wave distributed in a slit shape is adopted. This can also be used if it has a probe. The evanescent wave is
It is known that in addition to the above-mentioned minute aperture, it is also generated by a diffraction grating and total reflection.

[0047]

Since the optical memory device according to the first aspect of the present invention is configured as described above, the first and second probes are arranged opposite to each other with the optical recording medium sandwiched therebetween. Therefore, the evanescent wave having a large power can be concentrated in the minute area at the intersection of the first and second probes, and the intensity of the probe light can be improved. Therefore, highly reliable recording / reproducing of information can be guaranteed.

In the optical memory device according to the second aspect of the present invention, since the first and second probes are arranged so as to face each other so that their slit-shaped openings are orthogonal to each other, the evanescent wave It is possible to reduce the area of the concentrated region, and it is possible to record / reproduce information with high density.

In the optical memory device according to the third aspect of the present invention, the gap between the first and second probes is set so that the evanescent wave is not tunneled. It is possible to generate a large evanescent wave, and it is possible to record / reproduce information with high density and high reliability.

In the optical memory device according to the fourth aspect of the present invention, since light having coherence with each other is used as the probe incident light, the evanescent light generated by the first probe and the second probe is used. Since the optical power is increased as compared with the case of using light having no coherence, the waves interfere with each other, so that the evanescent wave can be generated more efficiently.

In the optical memory device according to the fifth aspect of the present invention, since the deflection direction of the probe incident light is the direction perpendicular to the longitudinal direction of each slit type opening, the transmitted light at the tip of the probe is It is possible to prevent the generation and to generate only the evanescent wave, and it is possible to record / reproduce information having a high S / N.

In the optical memory device according to the invention of claim 6 of the present application, the scanning means for scanning the first and second probes are made to perform mechanically independent one-dimensional scanning, respectively. The scanning means are not interfered with each other, the probe can be positioned with high accuracy, and the dynamic range of the probe scanning can be improved as compared with the two-dimensional scanning. Further, the mechanism is simpler than that of the two-dimensional scanning means, which leads to cost reduction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a first embodiment of an optical memory device of the present invention.

FIG. 2 is a schematic explanatory view showing a probe in the first embodiment of the optical memory device of the present invention.

FIG. 3 is an explanatory diagram showing recording pits in the optical recording medium in the first embodiment of the optical memory device of the present invention.

FIG. 4 is an explanatory diagram showing a schematic configuration of a second embodiment of an optical memory device of the present invention.

FIG. 5 is an explanatory diagram showing a schematic configuration of a conventional optical memory device.

[Explanation of symbols]

2 First probe 3 Second probe 4 Optical recording medium 5 First incident light 6 Second incident light 8,10 Tapered part 9,11 opening 12 Evanescent wave generation region by the first probe 13 Evanescent wave generation region by the second probe 14 recording areas 21 Laser device 22 Beam splitter 23-25 mirror

Claims (6)

(57) [Claims] 1. An optical memory device for recording / reproducing information on / from an optical recording medium by using evanescent light generated by a photon tunnel phenomenon, wherein a slit-shaped opening for generating evanescent light at a tapered tip end portion. And a second probe having a slit-shaped opening portion for generating evanescent light at a tapered tip portion, and the first and second probes are provided with slit-shaped openings. In a state where the parts intersect each other, the parts are arranged so as to face each other across the optical recording medium , the first probe and the second
Area where the evanescent wave generated from the probe intersects
An optical memory device, characterized in that the recording medium portion located at is a recording pit . 2. The optical memory device according to claim 1, wherein the first and second probes are arranged so as to face each other with their slit-shaped openings orthogonal to each other. apparatus. 3. The optical memory device according to claim 1, wherein the first and second probes have a gap that does not cause tunneling of evanescent light generated from each slit-shaped opening. , An optical memory device arranged opposite to each other. 4. The optical memory device according to any one of claims 1 to 3, wherein the first probe and the second probe are incident with lights having coherence with each other. . 5. The optical memory device according to any one of claims 1 to 4, wherein the first and second probes receive light having a deflection direction perpendicular to a longitudinal direction of each slit-shaped opening. An optical memory device characterized by being a thing. 6. The optical memory device according to claim 1, further comprising scanning means for independently one-dimensionally scanning the optical recording medium with each of the first probe and the second probe. An optical memory device characterized by.